This application pertains to the art of motion conversion mechanisms, and more particularly, to such mechanisms for converting axial motion into rotational motion. The invention is particularly applicable to valve rotators for imparting rotation to reciprocating valves on internal combustion engines and will be particularly described with reference thereto. However, it will be appreciated that the invention has broader aspects and may be used for imparting rotational movement to other reciprocating members.
It is common to rotate inlet or exhaust valves on internal combustion engines for such purposes as providing uniform heating to minimize distortion and onesided overheating, along with minimizing formation of carbonized oil residue on the head and stem sections of the valve.
The most common type of valve rotator operates for rotating the valve during opening movement thereof. One known rotator of this type includes first and second parts movable axially and rotatably relative to one another. Shiftable or movable members in the form of spherical balls are positioned between the two parts on inclined ramps and a spring disc normally holds the parts separated from one another. During opening movement of the valve, the force of the valve spring increases until it overcomes the biasing force of the spring disc and causes the parts to move toward one another so that the balls roll down the ramps for imparting relative rotation to the parts and rotate the valve.
In many instances, it is desirable and necessary to rotate the valve only during opening movement thereof to minimize wear which might occur by rotational movement of the valve head against the valve seat as the valve closes. However, in certain other applications, rotation of the valve during closing is desirable in order to wipe the valve head and seat. In one known arrangement of this type, the two parts of the rotator do not move axially relative to one another and a separate axially movable sleeve member is provided for acting on the spring disc outwardly of the two rotator parts. The spring disc normally forces the balls to the deep ends of the ramps against the biasing force of return coil springs acting on the balls for urging them toward the shallow ends of the ramps. During opening movement of the valve, the force of the valve spring increases and acts on the sleeve member for moving it axially to move the spring disc away from the balls and allow the coil springs to move the balls to the shallow ends of the ramps. As the valve moves toward its closed position and the force of the valve spring decreases, the sleeve member moves away from the spring disc which then acts upon the balls for rolling them down the ramps and imparting relative rotation to the parts. Therefore, the valve is rotating somewhat as it closes in order to wipe the valve head and valve seat of deposits, and insure good seating of the valve head against the valve seat.
In some instances, it is desirable to rotate the valve during both opening and closing movement thereof, with rotation in one direction of movement being greater than in the other so that the net positive or negative rotation progressively steps the valve rotatably. One known arrangement of this type combines the two valve rotators of the type previously described. The two rotator parts do not shift axially relative to one another and each has inclined ramps on which rollable balls are positioned. A spring disc positioned between the balls on the two parts is acted upon by a separate axially movable sleeve member which moves under the force of the valve spring. During opening movement of the valve, the force of the valve spring increases for axially moving the sleeve member to deform the spring disc which acts against the balls on one rotator part for moving them down their ramps and providing relative rotation in one direction. During such movement, the ball springs for the balls on the other part were free for shifting such balls to the shallow ends of their ramps. Upon closing movement of the valve, the sleeve member moves away from the spring disc due to the decreasing force of the valve spring so that the spring disc forces the balls on the other part down their inclined ramps to impart relative rotation in an opposite direction. In such an arrangement, a multiple spring disc is required in order to obtain a greater angular degree of relative rotation in one direction than in the other. An arrangement of this type is extremely complicated because it requires an additional sleeve member, along with multiple spring discs and balls positioned on inclined ramps on both of the rotator parts.
Another arrangement for rotating a valve different degrees of angular movement during opening and closing movement thereof is disclosed in U.S. Pat. No. 2,935,058 issued May 3, 1960, to Dooley. In the Dooley arrangement, the two rotator parts are mounted in such a manner that a separating force applied thereto would act against the valve spring in the direction of valve opening movement, rather than in the direction of valve closing movement. This means that the biasing means for axially separating the parts cannot have a magnitude intermediate the valve closed and valve open forces applied by the valve spring because the biasing means would then tend to hold the valve open and prevent complete closing thereof unless extremely accurate adjustment of the rocker arm was maintained.
The Dooley arrangement includes one rotator part 8 which is fixed against axial movement relative to valve stem 4 but is free to rotate relative thereto. Another rotator part 10 is movable toward part 8 and also rotates relative to part 8 for imparting rotation to the valve during opening movement thereof. The valve spring in Dooley is coiled in such a manner that rotation of part 10 by rolling movement of the balls down the ramps also tends to rotate part 8 which then applies torque to the valve spring for winding it up and storing energy during opening movement of the valve. During closing movement of the valve, the energy stored in the valve spring is released as the valve spring unwinds so that part 8 is rotated in an opposite direction to that imparted thereto by the rolling balls, and such rotation presumably acts through the balls to rotate part 10 and the valve in an opposite direction during closing movement thereof to an angular degree less than that imparted thereto during opening movement thereof. The Dooley arrangement is very complicated, and relies upon relatively unreliable winding and unwinding movement of the valve spring. The valve spring is not really a part of the rotator mechanism itself. The relative winding strength of the valve spring may vary due to differences in heat treating and other manufacturing operations so that reliable reverse rotation a predetermined angular degree is not always possible. It is also possible for workers to assemble the valve spring reversed so it would not coil up to store energy during opening movement of the valve. Relying upon stored energy in the valve spring also makes it necessary for part 8 to rotatably act in a direction for rolling the balls up the ramps during closing movement of the valve. Therefore, the balls may simply roll or slide all the way up the ramps without imparting any reverse rotation to the valve, or have such reverse rotation completed before the valve is just closing so it will not rotatably wipe against the valve seat.